Numerous products are made of matrices, such as resin matrices, which are reinforced with reinforcement fibers. The reinforcement fibers can be introduced into the product in a variety of ways. From the standpoint of industrial production, a major method of introducing fibers into matrices involves the formation of a mat of reinforcement fibers. The reinforced products, generally referred to as "composites", can be used for numerous end uses, including automobile, industrial and domestic equipment as well as electronic components. The reinforcement fibers can be of any material, length, diameter or shape suitable to provide the resin matrix with superior properties, such as strength, stiffness and fire retardancy. Typical reinforcement fibers include mineral fibers, such as glass fibers, organic fibers, such as nylon fibers, and natural fibers, such as flax or sisal. The mineral reinforcement fibers typically have sizes or coatings, involving such polymers as polyvinyl acetate, polyurethane or epoxy.
The formation of a reinforcing mat, and thus the distribution of reinforcement fibers onto a substrate or collection surface, can be accomplished in several ways. The fibers can be mixed with a liquid and formed into a slurry, which is then moved over a porous conveyor where the liquid is removed. This product is known as a wet process mat or wet laid mat. A problem with the wet process is that it requires enormous equipment with associated very high capital investments, and it consumes a significant amount of energy to drive the liquid from the system. The process also requires extensive cleaning to protect the environment.
Another process for distributing fibers is to air lay or air blow them onto a collection surface. The desired effect is uniform distribution and a random orientation, much like the randomness of a snowstorm. A problem with the air laid mat process is that it is difficult to control metering of the fibers (the output rate as a function of time) to allow uniformity along the line axis or machine direction of the mat. It is also difficult to achieve uniform distribution of the fibers transverse to the line direction or machine direction, particularly when the input material is in the form of discontinuous fibers of high aspect ratio (length versus diameter). A uniform air laid distribution of fibers is particularly difficult for wide collection surfaces, such as surfaces wider than one meter.
One problem common to most fiber distribution operations is that the fibers tend to agglomerate or cling together in clumps or tufts, thereby creating areas of high fiber density. This is a problem for both wet laid mats and air laid mats. Some fiber distribution systems are configured to pick apart the clumps or high concentration areas of fibers by pulling apart the clumps of fibers with pins. Even where the fiber distribution apparatus is designed to pick apart the fibers, there is still a great difficulty in producing a uniform distribution of fibers randomly oriented on a collection surface. Also, distribution systems using pins to pick apart or transport fibers have problems with fibers becoming caught or jammed between the pins, and it is difficult to remove the fibers from the pins. Even the use of slippery coatings on the fibers has not solved this problem. Further, trying to distribute long fibers, i.e., longer than about 2 cm, is even more troublesome because the greater amount of intertwining of the long fibers around the pins makes it more difficult to remove the fibers from the pins.
Accordingly, there is a need for a system that can produce a uniform distribution of fibers to make reinforcement mats and reinforced sheet like products. Such system should be able to provide a uniform distribution of fibers on wide collection surfaces, such as those wider than one meter. Also, ideally the system would avoid the use of liquids to avoid high capital investments and energy costs as well as costly pollution control systems. Further, the system should be able to evenly distribute typical long fibers, having a length within the range of from about 2 to about 10 cm.